The present disclosure relates generally to ac/dc converters, particularly to rectifier topologies, and more particularly to discontinuous conduction mode (DCM) boost rectifiers and methods of modulation the same.
There are several topologies and control methods to realize medium to high power front end converters. In general, it is desirable for these rectifiers to operate at a high power factor (PF) and with a low total harmonic distortion (THD), especially when the converter is connected to the electrical grid of a utility. Typical applications for these converters include: UPSs (Uninterruptible Power Supplies), frequency converters and drives. A well known topology is the Two Switch Three Level DCM (Discontinuous-Conduction-Mode) Boost Rectifier. This topology is quite popular in three phase transformerless UPSs for its excellent performance/cost ratio. With just two active switches in the booster section it is possible to reach very good PF and THD on the overall load range. Also, the efficiency of the converter is very high (typically 98%) with respect to more complex and expensive active IGBT (Insulated Gate Bipolar Transistor) rectifiers. The modulation strategy for the switches has an important influence on the overall behavior of the rectifier, in particular on the input THD and on the stress on the IGBTs (peak current, blocking voltage, and losses, for example). Several modulation strategies have been proposed and are currently used in industrial products. However, to reduce the THD possible with the existing art, one has to consider alternative topologies or additional passive filters. Existing alternative topologies have other drawbacks, such as stress on the IGBT's, and whereas additional passive filters may improve the THD, they do so on just a limited load range, and introduce potential resonance when a generator is used in place of the grid.
Accordingly, and to further the technical arts relating to DCM Boost Rectifiers, it would be advantageous to determine an optimal modulation strategy that minimizes a desired cost function.